The invention relates to an electric motor comprising a first part and a second part which are movable with respect to each other, wherein the first part comprises a foil-shaped insulating substrate on which a plurality of series-connected spiral-shaped patterns of conductor tracks are provided, each pattern comprising two main sections with substantially straight and parallel conductor tracks having first and second ends and two intermediate sections with conductor tracks which respectively mutually connect the first ends of the two main sections and mutually connect the second ends of the two main sections, said intermediate sections having a center area halfway between the first ends of the two main sections and halfway between the second ends of the two main sections, respectively, and wherein the second part comprises a permanent magnet unit for generating a magnetic field at the location of the conductor tracks.
The invention also relates to a data storage unit comprising a support for at least one information carrier, an electric motor for rotating the support about an axis of rotation, and a scanning unit for scanning the information carrier.
A data storage unit and an electric motor of the kinds mentioned in the opening paragraphs are known from EP-B-0 764 357. The known data storage unit is a hard disc drive, wherein a plurality of hard discs are arranged in mutually parallel positions on the rotatable support. The known electric motor, which is used to rotate the support about the axis of rotation, comprises a circular-cylindrical stator body comprising three layers of the foil-shaped insulating substrate. The patterns of conductor tracks form a three-phase electric coil system, wherein each layer of the stator body comprises one of the respective phases. The conductor tracks constitute relatively thin copper tracks, which are provided on the substrate by means of an etch process. The known electric motor further comprises a circular-cylindrical rotor body, which is fastened to the support and comprises a circular-cylindrical permanent magnet and a circular-cylindrical closing yoke, the stator body being arranged in a circular-cylindrical gap which is present between the magnet and the closing yoke. The intermediate sections of the patterns of conductor tracks of the known motor have substantially straight, parallel conductor tracks which extend perpendicularly to the conductor tracks of the main sections, so that the patterns of conductor tracks have a rectangular shape. The conductor tracks of the main and intermediate sections further have identical, constant widths.
A disadvantage of the known data storage unit and the known electric motor used therein is that, when a predetermined constant electric voltage is supplied to the coil system of the motor, the rotational speed of the motor strongly decreases when the external mechanical torque exerted on the motor about the axis of rotation increases. As a result, the voltage supplied to the motor must be strongly increased to maintain a predetermined speed of the motor at an increased value of the external torque.